Apex domains cannot have CNAME records.
Question and response
Question
dig rupert.net. NS
Answer
rupert.net. 2 NS ns3.rupert.net.
rupert.net. 2 NS digby.citytel.net.
Authority
The response has no authority records.
Additional
ns3.rupert.net. 2 A 209.145.111.62
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0